This invention is an improvement of application Ser. No. 370,163, filed June 14, 1973 and application Ser. No. 396,494, filed Sept. 12, 1973 which are hereby incorporated by reference.
Rectilinear scanners use a single line of radiation and are moved along a square wave path to sense patterns of radiation. The rectilinear scanner has the advantage of being able to view the entire body of a patient, and the disadvantage of taking about 45 minutes to do so. Patient discomfort, movement and signal inaccuracies often result from the time necessary for such a scan.
For small area studies, what has commonly become known as a scintillation camera has a distinct advantage over a rectilinear scanner. The camera views an entire area of radiation simultaneously and, thus, greatly reduces the time necessary for the patient to remain motionless. A previous disadvantage of a camera over the rectilinear scanner was its inability to study large sections of radiation. A natural evolution for the camera was its transition into a type of camera-scanner in which the area of camera view traversed the section of radiation, e.g., a whole body scan. Because of the greater area of the detecting head of the scintillation camera as compared to a rectilinear scanner, the time of an entire body scan was reduced from about 45 minutes to 10 minutes. This significant decrease in the amount of time is a substantial benefit since it increases potential patient utilization and permits greater patient comfort and accuracy.
One of the problems encountered in having a camera scan is the correlation of data. The detector head of the camera is not large enough to encompass the entire width of some sections of radiation and, as a result, the camera must make multiple passes in order to complete a scan. Correlation of the information from the multiple passes must be precise or artificial indications of radiation, called artifacts, will appear. In particular, if the passes overlap, some areas will be reviewed twice and if the passes are separated, areas could be missed.
In order to reduce the artifacts from multiple passes, the present invention has derived a means for correlating the adjacent sides of a scanning area. The scanning area is defined by an electronic mask which allows the camera to display only the scintillations in a given area. The area may be a rectangle, a parallelogram, square or other shape. This invention provides for the oscillation of the sides parallel to the longitudinal sides of the pass at a given frequency and thus eliminates distinct edges to information received during the pass. When the second or subsequent pass occurs, the same oscillation is used and the information is matched with that of the first pass so that the adjacent edges combine in a feathered effect which does not give detectable artifacts or lines of demarcation.
The scanning camera also must provide uniform exposure of the detector head to the section of radiation under study. In order to equalize radiation exposure, the detector head of the camera previously had to start beyond the initial end of the section of radiation and pass completely over the other end. Thus, facilities were required to permit the detector head to move completely beyond the radiation under study. The overhang of the detector head was an annoying problem in the hospital. Space utilization on either side of the scanning camera became impossible and physical contact with the overhanging section could cause inaccuracies in tests and potential damage to the camera and injury to the operator.
In order to avoid camera overhang, the present invention proposes to limit the mechanical movement of the camera head to a path above the section of radiation it views. That is, the camera head stays above the cot on which the patient is lying. While the undesirable overhang of the camera is avoided, compensation must be made for the reduced exposure time of the head to the ends of the section of radiation. A simple mechanical pass moves the head away from its starting position before adequate radiation can be observed. In order to provide the same amount of exposure of the head to all areas of the section of radiation, an electronic scan is provided at each end of a mechanical scan. When the first pass is initiated, an electronic scan occurs. It operates similar to a sliding lid gradually opening on a box. The electronic scan is timed to correspond with the mechanical scan so that no artifacts are created by the transfer from electrical to mechanical scans. When the electronic scan is complete, the head mechanically moves and traverses the length of the section of radiation under consideration. When the head reaches the end of the section of radiation, instead of having to pass completely over it as in the prior art, it is able to stop and another electronic scan continues in a manner similar to closing a sliding lid on a box container. At the end of the first pass, the support means for the section of radiation, i.e. the cot on which the patient is lying, is indexed or moved transverse to the longitudinal scan direction. The electronic scan again occurs but in the opposite direction, the mechanical scan is actuated, the head moves the length of the section of radiation and an electronic scan again occurs. Similar additional passes can be made to complete the scan.